Nitrogen, phosphorus and potassium recycling in an agroforestry ecosystem of Huanghuaihai Plain: with Paulownia elongata intercropped wheat and maize as an example

The studies show that in the whole community, P is deficient, and N and K are basically balanced. N, P and K are accumulated in plant tissues and litters, but depleted in soil. N and P contents in surface soil(0—20 cm) are the main factors affecting crop growth, and P contents in 20 80 cm soil layer is the major affecting Paulownia elongata growth. The absorption coefficients of N, P and K in the communities are 0 078, 0 014 and 0 052 respectively, their utilization coefficients are 0 95, 0 90 and 0 94, and the recycling coefficients are 0 042, 0 05 and 0 063 respectively.

Impact of recycling improvement on the life cycle of phosphorus

Access to natural resources is increasingly more difficult and more costly, partly due to their economic significance and to continuous increase of their global consumption in the recent years. In the case of phosphorus (P), which is a critical raw material, geological distribution of its primary nonrenewable source (phosphate rock) is concentrated in particular regions leading to high supply risk of this raw material. In Europe (EU-28), where phosphate rock reserves are scarce, import of phosphorus has been the main source of supply. It means that Europe relies highly on the foreign exporters. From decision makers' perspective, recycling of phosphorus was taken into account as one of the possible solutions to decrease the dependence on imports and extraction of reserves. The question, however, is to what extent does the recycling of phosphorus help in reducing the reliance on typical supply resources? Hence, the main objective of this paper is to quantify the dynamic flow of phosphorus and show potential benefits of its recycling in Europe. This article presents a system dynamics model for representation of the element P flow and helps to quantify to what extent the recycled phosphorus could mitigate its criticality. Analysis of the results supports previous studies indicating the high reliance ofEU on P imports, estimating around 96% as the reliance percentage on imports. The results imply that improving P recycling has the potential to decrease the level of P imports to a certain extent, which may reach 79%.

BIOGEOCHEMICAL PROCESSES OF PHOSPHORUS AND SILICON IN SOUTHERN BOHAI SEA SURFACE SEDIMENTS

Based on the author’s previously obtained results on P and Si forms in southern Bohai Sea surface sediments,this study mainly foucusing on the controlling factors, existence forms, and biogeochemical processes of P and Si showed that the transferable forms of phosphorus in sediments were mainly controlled by the mineralization of organic matters and the reduction of high valence iron; whereas the transferable forms of silicon were possibly controlled by the dissolution and precipitation as well as biochemical processes of living organisms.

Preparation of Wastewater Phosphorus Removal Materials by Dry FGD Ash Produced from Iron Industry

Dry FGD （Flue Gas Desulfurization） ash produced from iron industry is used as the main raw material to prepare recyclable wastewater phosphorus removal materials through non-burned process. By testing various formulae and preparation conditions, this paper discusses the different results of phosphorus removal efficiency of the samples to figure out which is the best formula. Spectrophotometric determination with phosphor molybdenum blue is used to determine the phosphorus concentration. Flexural strength and porosity are determined correspondingly as well. By applying SEM and EDS techniques, the microstructure change of the sample is characterized after phosphorus removal. The best formula is that prepared by using 84wt% of FGD ash and 16wt% of cement. The flexural strength of the sample is 12.15 MPa, and the porosity is 20.5%. Microstructure analysis indicates that phosphate adsorption occurs mainly on the surface of the material.

Optimization of denitrifying phosphorus removal in a predenitrification anaerobic/anoxic/post-aeration+nitrification sequence batch reactor(pre-A_(2)NSBR)system:Nitrate recycling,carbon/nitrogen ratio and carbon source type

Because the efficiency of biological nutrient removal is always limited by the deficient carbon source for the low carbon/nitrogen(C/N)ratio in real domestic sewage,the denitrifying phosphorus removal(DNPR)was developed as a simple and efficient method to remove nitrogen and phosphorous.In addition,this method has the advantage of saving aeration energy while reducing the sludge production.In this context,a pre-denitrification anaerobic/anoxic/post-aeration+nitrification sequence batch reactor(pre-A_(2)NSBR)system,which could also reduce high ammonia effluent concentration in the traditional two-sludge DNPR process,is proposed in this work.The pre-A_(2)NSBR process was mainly composed of a DNPR SBR and a nitrifying SBR,operating as alternating anaerobic/anoxic/post-aeration+nitrification sequence.Herein,the long-term performance of different nitrate recycling ratios(0-300%)and C/N ratios(2.5-8.8),carbon source type,and functional microbial community were studied.The results showed that the removal efficiency of total inorganic nitrogen(TIN,including NH4^(+)-N,NO_(2)^(-)-N,and NO_(3)^(-)-N)gradually increased with the nitrate recycling ratios,and the system reached the highest DNPR efficiency of 94.45% at the nitrate recycling ratio of 300%.The optimum C/N ratio was around 3.9-7.3 with a nitrogen and phosphorus removal efficiency of 80.15%and 93.57%,respectively.The acetate was proved to be a high-quality carbon source for DNPR process.The results of fluorescence in situ hybridization(FISH)analysis indicated that nitrifiers and phosphorus accumulating organisms(PAOs)were accumulated with a proportion of 19.41%and 26.48%,respectively.

A Modified Oxidation Ditch with Additional Internal Anoxic Zones for Enhanced Biological Nutrient Removal

A novel modified pilot scale anaerobic oxidation ditch with additional internal anoxic zones was operated experimentally, aiming to study the improvement of biological nitrogen and phosphorus removal and the effect of enhanced denitrifying phosphorus removal in the process. Under all experimental conditions, the anaero- bic-oxidation ditch with additional internal anoxic zones and an internal recycle ratio of 200% had the highest nutrient removal efficiency. The effluent NH4 -N, total nitrogen （TN）, PO3 -P and total phosphorus （TP） contents were 1.2 mg.L-1, 13 mg.L 1, 0.3 mg.L -1 and 0.4 mg.L-1, respectively, all met the discharge standards in China. The TN and TP removal efficiencies were remarkably improved from 37% and 50% to 65% and 88% with the presence of additional internal anoxic zones and internal recycle ratio of 200%. The results indicated that additional internal anoxic zones can optimize the utilization of available carbon source from the anaerobic outflow for denitrification. It was also found that phosphorus removal via the denitrification process was stimulated in the additional internal anoxic zones, which was beneficial for biological nitrogen and phosphorus removal when treating wastewater with a limited carbon source. However, an excess internal recycle would cause nitrite to accumulate in the system. This seems to be harmful to biological phosphorus removal.

Impact of Rice-Catfish/Shrimp Co-culture on Nutrients Fluxes Across Sediment-Water Interface in Intensive Aquaculture Ponds

Exchange of nitrogen and phosphorus across sediment-water interface plays an important role in the management of nutrient recycling in the aquaculture pond. In this study, a plot experiment was conducted to study the effect of rice-catfish/shrimp co-culture on the micro-profile of oxygen (O2), pH and nutrient exchange across sediment-water interface in the intensive culture ponds. The results showed that rice-catfish co-culture increased the concentration and penetrating depth of O2, but decreased the pH value across the sediment-water interface, compared with catfish monoculture. Additional rice cultivation significantly reduced the flux rates of ammonium (NH4+) and nitrate (NO3-) across sediment-water interface in the catfish and shrimp ponds. The flux rates of NO2 - and soluble phosphorus (PO43-) showed no significant difference between rice-catfish/shrimp co-culture ponds and catfish/shrimp monoculture ponds. Rice only affected the dissolved inorganic nitrogen and phosphorus fractions in the sediment. The concentrations of NH4 + were significantly lower in the sediment of co-culture ponds than in the monoculture ponds. Additional rice cultivation also significantly reduced the content and percentage of dissolved inorganic phosphorus in the sediment of catfish ponds.

Combined effects of volume ratio and nitrate recycling ratio on nutrient removal,sludge characteristic and microbial evolution for DPR optimization

The optimization of volume ratio(V_(An)/V_(A)/V_(0))and nitrate recycling ratio(R)in a two-sludge denitrifying phosphorus removal(DPR)process of Anaerobic Anoxic Oxic-Moving Bed Biofilm Reactor(A^(2)/O-MBBR)was investigated.The results showed that prolonged anaerobic retention time(HRT An:1.25→3.75 hr)exerted favorable effect on chemical oxygen demand(COD)removal(57.26%→73.54%),poly-β-hydroxyalkanoates(PHA)synthesis(105.70→138.12 mg COD/L)and PO_(4)^(3-)release(22.3→38.9 mg/L).However,anoxic retention time(HRT A)and R exhibited positive correlation with PHA utilization(43.87%-81.34%)and denitrifying phosphorus removal(DPR)potential(NO_(3)-/PO^(3-)_(4):0.57-1.34 mg/mg),leading to dramatical TN removal variations from 68.86%to 81.28%.Under the V An/V A/V O ratio of 2:6:0,sludge loss deteriorated nutrient removals but the sludge bioactivity quickly recovered when the oxic zone was recovered.The sludge characteristic and microstructure gradually transformed under the dissolved oxygen(DO)control(1.0-1.5→1.5-2.0 mg/L),in terms of sludge volume index(SVI:194→57 m L/g VSS),median-particle-size(D 50:99.6→300.5μm),extracellular polymeric substances(EPS)(105.62→226.18 mg/g VSS)and proteins/polysaccharides(PN/PS)ratio(1.52→3.46).Fluorescence in situ hybridization(FISH)results showed that phosphorus accumulation organisms(PAOs)(mainly Cluster I of Accumulibacter,contribution ratio:91.79%-94.10%)dominated the superior DPR performance,while glycogen accumulating organisms(GAOs)(mainly Competibacter,contribution ratio:82.61%-86.89%)was responsible for deteriorative TN and PO_(4)^(3-)removals.The optimal HRT A and R assembled around 5-6.5 hr and 300%-400%based on the PHA utilization and DRP performance,and the oxic zones also contributed to PO_(4)^(3-)removal although it showed low dependence on DO concentration and oxic retention time(HRT_(0)).

Kinetics of Reaction-Crystallization of Struvite in the Continuous Draft Tube Magma Type CrystallizersmInfluence of Different Internal Hydrodynamics

A laboratory-scale reaction-crystallization process of struvite synthesis from diluted water solution of Mg^2＋, NH^＋ 4 and PO3- ions was studied. The research covered the tests of two original constructions of continuous jet-pump Draft Tube Magma （DTM）-type crystallizers with internal circulation of suspension （upward/downward）. Interactions between constructional, hydrodynamic and kinetic factors were established and discussed. Nucleation and linear growth rates of struvite crystals were calculated on the basis of population density distribution. Kinetic model of idealized Mixed Suspension Mixed Product Removal （MSMPR） crystallizer considering the size-dependent growth mechanism was applied （Rojkowski hyperbolic equation）. For comparison purposes the kinetic data corre- sponded to a simpler, continuous draft tube-type crystallizer equipped with propeller agitator were analyzed. It was concluded that crystal product of larger size was withdrawn from the jet-pump DTM crystallizer of the descending flow of suspension in a mixing chamber.

Research Progress on Energy Plants in Piggery Wastewater Treatment

Large-scale pig-raising can discharge a great deal of wastewater,which contains high content of organic matter,ammonia nitrogen and suspended solids.The improper treatment of the piggery wastewater can lead to serious environmental problems. As a liquid fertilizer,piggery wastewater is relatively low in fertilizer efficiency and high in transportation cost,so it is very necessary to treat it in situ. Energy plants have the advantages of rapid growth,large biomass,strong tillering ability and developed root system. Therefore,energy plants can be used to absorb and transform the pollutants( like nitrogen and phosphorus) in piggery wastewater into the components of plants,as well as form the rhizosphere environment which is conducive to microbial growth,so as to enhance the effects of nitrogen and phosphorus removal. The obtained energy plants can be recycled as the raw materials for biogas to increase the production of biogas,which brings economic benefits while solving the environmental problems caused by piggery wastewater.

Reaction Crystallization of Struvite in a Continuous FB MSZ Type Crystallizer with Jet Pump Driven by Compressed Air

The results of struvite reaction crystallization from diluted water solutions of phosphates （V） （0.20 mass% of PO43-） by means of magnesium and ammonium ions are presented. Continuous FB MSZ crystallizer with jet pump driven by compressed air was used. Influence of pH and mean residence time of suspension on the crystal product quality was determined. Increase in pH from 9 to 11 resulted that mean crystal size decreased nearly two-time： from 27.1 to 15.1μm for mean residence time of suspension 900 s. Elongation of this time from 900 to 3,600 s influenced struvite crystal size advantageously-it increased from 27.1 to 41.2 μm at pH 9. From the population density distributions nucleation and growth rates of struvite were calculated based on the simplest SIG model of mass crystallization kinetics in MSMPR crystallizer. Linear growth rate ofstruvite crystals decreased nearly two-time with the increase in environment pH from 9 to 11, and more than 2.5-time with the elongation of mean residence time of crystal suspension in a crystallizer from 900 to 3,600 s from 1.34× 10-8 m/s （pH 9, τ= 900 s） to 2.60×10-9 m/s （pH 11, τ= 3,600 s）.

Utilization and management of organic wastes in Chinese agriculture:Past,present and perspectives

Recycling and composting of organic materials such as animal waste, crop residues and green manures has a long tradition in China. In the past, the application of organic manures guaranteed a high return of organic materials and plant mineral nutrients and thus maintained soil fertility and crop yield. As a result of rapid economic development coupled with the increasing urbanization and labour costs, the recycling rate of organic materials in Chinese agriculture has dramatically declined during the last two decades, in particular in the more developed eastern and southeastern provinces of China. Improper handling and storage of the organic wastes is causing severe air and water pollution. Because farmers are using increasing amounts of mineral fertilizer, only 47% of the cropland is still receiving organic manure, which accounted for 18% of N, 28% of P and 75% of K in the total nutrient input in 2000. Nowadays, the average proportion of nutrients (N+P+K) supplemented by organic manure in Chinese cropland is only 35% of the total amount of nutrients from both inorganic and organic sources. In China, one of the major causes is the increasing de-coupling of animal and plant production. This is occurring at a time when 're-coupling' is partly being considered in Western countries as a means to improve soil fertility and reduce pollution from animal husbandry. Re-coupling of modern animal and plant production is urgently needed in China. A comprehensive plan to develop intensive animal husbandry while taking into account the environmental impact of liquid and gaseous emissions and the nutrient requirements of the crops as well as the organic carbon requirements of the soil are absolutely necessary. As a consequence of a stronger consideration of ecological aspects in agriculture, a range of environmental standards has been issued and various legal initiatives are being taken in China. Their enforcement should be strictly monitored.

Roller-coaster atmospheric-terrestrial-oceanic-climatic system during Ordovician-Silurian transition:Consequences of large igneous provinces

The Ordovician-Silurian transition(OST)hosted profound and frequent changes in the atmospheric-terres trial-oceanic-climatic system(ATOCS).Previous studies have found contrasting stages for such changes,primarily based on hiatus-interrupted sections.However,the dominant driving factors and mechanisms reconciling such frequent changes remain controversial.Mercury isotopes,which undergo both massdependent and mass-independent fractionation,can provide critical insights into the deep-time ATOCSs,especially for those impacted by large igneous provinces(LIPs)events.Here,we build a highresolution multi-proxy record of Hg(concentrations and isotopic compositions)combined with organic carbon isotopes(δ^(13)Corg)and whole-rock geochemical data(including trace elements and phosphorus)from continuous cores in the Yangtze Platform,South China.Our data,combined with reported ones,indicate the occurrence of LIP eruptions against localized volcanism,and four successive,yet contrasting stages of ATOCSs during the OST.Moreover,we identified the coupling between two-pulse LIP magmatism and extreme ATOCSs,each with special pCO_(2),weathering rate,primary productivity,redox condition,climatic mode,and biotic evolution.For stage I,the first pulse of LIP magmatism triggered global warming,enhanced terrestrial weathering,oceanic acidification,eutrophication,anoxia,P recycling,and thereby widespread deposition of black shales.During stage II,the Hirnantian glaciation and oxygenation arose from the intense chemical weathering and black shale deposition of stage I;slashed terrestrial weathering and oceanic oxygenation facilitated CO_(2) accumulation.In stage III,another pulse of LIP magmatism triggered the de-glaciation,and the ATOCS was largely similar to that of stage I.This led to another round of oxygenation and positive d13Corg excursion in stage IV.Compared with the environmental pressure by the peculiar ATOCS of each stage,their transitions might have been more devastating in triggering the prolonged Late Ordovician Mass Extinction(LOME).Moreover,limited biotic recovery was possible in the later portion of stages I and III.The multi-proxy study of continuous strata of the OST provides an excellent framework for better illuminating LIPs’essential role in driving the“roller-coaster”behavior of the ATOCS and thus biotic crisis during the pivotal period of the OST.

Wengfu Came on Stream AHF Unit Demonstration for the Utilization of Fluorine Resources in Phosphate Fertilizers Production

The 20 000 t/a anhydrous hydrogen fluo-ride(AHF)unit in Guizhou Wengfu Lantian Fluorine Chemical Co.,Ltd.subordinate to Wengfu(Group)Company Limited has recently carried out successful wet commissioning.It shows that the first project worldwide using byproduct fluorosilicic acid in the phosphoric acid production to produce AHF has started commercial production.The unit employs the advantage of phosphorus resources in Wengfu,uses byproduct fluorosilicatic acid in the phosphoric acid production as raw material and effectively recovers fluorine resources.Byproduct sulfuric acid gener-ated in the production can be recycled